1. Field of the Invention
The present invention relates to a disk unit, having a head suspension, for supporting a head for writing and/or reading information on a disk.
2. Description of the Related Art
A head suspension, which is generally used in a disk unit such as a floppy disk drive unit or a magnetic disk unit, includes a support beam, a spacer, and a gimbal. The gimbal is formed with more flexibility than that of the support beam and is mounted on one end (free end) of the support beam. On the surface of the gimbal is mounted a magnetic head slider, which is provided with a magnetic head for writing and/or reading information. The spacer is formed with a boss and is mounted on the other end of the support beam. The head suspension is connected to a carriage arm of the disk unit through the boss.
When a driving force from an actuator such as a voice coil motor is transmitted to the carriage arm, the head suspension supporting the head slider thereon is driven via the carriage arm so that the head of the head slider can write and/or read information data on a magnetic disk (storage medium) having a magnetic thin film on its surface.
A spring force (an urging force) applied by the support beam of the head suspension urges the head slider toward the surface of the disk, while a flying force or floatation force (positive pressure), generated by an air flowing between the surface of the disk and the surface of the head slider during rotation of disk, is exerted on the head slider to move it away from the surface of the disk. The balance of these two forces, the spring force and the flying force, results in the head slider flying above the disk with a gap (typically, 20 nm) between the surface of the disk and the surface of the head slider.
Recently, an increased storage capacity has been required of a disk unit having such the head suspension. This requires a decreased gap between the surfaces of the disk and the head slider for writing data on the disk with a higher density. As mentioned above, the gap between the surfaces of the head slider and the disk (i.e., the flying height) depends upon the balance of the spring force applied by the head suspension and the flying force (positive pressure) generated by the air flowing between the surfaces of the disk and the head slider. Therefore, the spring force applied by the head suspension should be increased in order to decrease the gap. On the other hand, an increased spring force often leads to an increased risk of damage to the surface of the disk or the head slider when the head slider happens to contact with the disk. Therefore, it is desirable to make the spring force as small as possible.
In order to achieve a small flying height under such small spring force, a negative pressure slider has been developed. This negative pressure slider generates a negative pressure, acting in a direction opposite to the flying force (positive pressure), between the slider and the disk by utilizing a diffuser effect, and thereby makes it possible to obtain a smaller gap (flying height) between the surfaces of the slider and the disk under small spring force.
In the case of using the negative pressure slider, it is generally required to maintain the gap between the surfaces of the slider and the disk smaller than the predetermined distance. This is because there is a limiting distance at which the negative pressure slider does not generate negative pressure. Thus, in vicinity of this limit distance, the negative pressure slider has a bistable flying characteristic, i.e., a characteristic which allows the slider to be stable in two different flying height, i.e., one flying height where there is a balance between the spring force and the flying force generated by positive pressure and the other flying height where there is a balance among the spring force, the acting force generated by the negative pressure, and the flying force generated by positive pressure. Therefore, in the use of the negative pressure slider, in order to avoid this bistable flying state, it is typical that a spring force from the head suspension must be adjusted in response to a distance between the surface of the disk and the position of the head suspension mounted to the carriage arm so as to obtain a sufficient spring force to maintain the negative pressure slider and the disk in a distance closer than a distance which ensures the generation of a negative pressure between them.
In a hard disk unit, if the rotation of a disk is stopped, a magnetic head slider will not receive a flying force (positive pressure) and will contact the surface of the disk. Therefore, it is required to protect a ring-shaped data zone of the disk, for data to be recorded, from the head slider when the disk is not rotated. One way of protecting the data zone is to take the head slider out of the data zone when the disk is not rotating. Suitable mechanisms are divided into two major types; a CSS (contact start stop) type and a ramped loading type. Recently, the ramped loading type mechanism has been used in many cases.
The ramped loading type mechanism includes a loading bar at the tip of the head suspension. When the disk is not rotating, the head suspension is moved such that the loading bar can ride over a ramp located outside the outer periphery of the disk. This makes the head slider move away from the surface of the disk (unload) and allows it to escape from the data zone of the disk to the outside of the disk. On the other hand, after the disk starts rotating, the head suspension is moved such that the loading bar can move down from the ramp. This makes the head slider move close to the surface of the disk (load) and allows it to move to the data zone of the disk.
In loading, a spring force from the head suspension is balanced with a reaction force from the surface of the ramp while the loading bar at the tip of the head suspension is positioned on the surface of the ramp. However, the reaction force is not exerted on the loading bar after the loading bar is detached from the ramp. Thus, at the moment the loading bar is detached from the ramp, the distal end of the head suspension is moved toward the surface of the disk, in a short time, by its own spring effect. This causes a problem of vibration of the head suspension. This vibration of the head suspension may result in the head slider contacting the surface of the rotating disk because of the temporarily decreased flying height of the head slider mounted on the distal end of the head suspension.
Moreover, since a greater rotation speed of the disk generates a greater level of impact energy at the contact of the head slider with the disk, the loading of the head slider at the outer area (the area near to the outer periphery) of the disk produces a greater level of impact energy. Thus, a disk unit that employs a ramped loading type mechanism, in which the head slider loads to the disk at its outer area, suffers from the risk that the contact of the head slider with the disk causes fatal damage to both devices.
An object of the present invention is therefore to reduce the vibration of a head suspension occurring on loading of a head slider to a disk while decreasing a level of impact energy generated by the contact of the head slider with the disk and thereby reducing the risk of causing damage to the disk and to the head slider.
To achieve the object, the present invention provides a disk unit having a head suspension which can load a head slider to a disk after moving the head slider to an inner area (an area adjacent to the center) of the disk.
In accordance with a first aspect of the present invention, there is provided a head suspension of a disk unit adapted for supporting a head for writing and/or reading information on a disk mounted in the disk unit and applying force to the head in a direction substantially vertical to the surface of the disk, which includes a first beam having a free end for the head to be mounted at and a proximal end opposite to the free end; a second beam arranged in opposed position to the first beam and having two ends, one end thereof positioned on the side of the free end of the first beam and fixed to the first beam, the other end thereof spaced apart from the first beam; and a moving means for longitudinally moving the first beam and the second beam relative to each other.
In accordance with a second aspect of the present invention, there is provided a disk unit which includes a disk for storage of information, a head for writing and/or reading information on the disk, a driving unit for moving the head between an area above the disk and an area outside the outer periphery of the disk, and a head suspension for supporting the head and applying force to the head in a direction substantially vertical to the surface of the disk. The head suspension includes a first beam having a free end for the head to be mounted at and a proximal end opposite to the free end, a second beam arranged in opposed position to the first beam and having two ends, one end thereof positioned on the side of the free end of the first beam and fixed to the first beam, the other end thereof spaced apart from the first beam, and an moving means for longitudinally moving the first beam and the second beam relative to each other.
This arrangement of the head suspension according to the present invention makes it possible to change the force applied to the head supported on the head suspension in the direction substantially vertical to the surface of the disk by longitudinally moving the first beam relative to the second beam. This change of the force applied to the head allows for adjustably changing the flying height of the head with respect to the surface of the disk.
Preferably, one of the proximal end of the first beam and the other end of the second beam includes a longitudinally movable end, which can move between a first position and a second position where the movable end is farthest away from the disk. More preferably, the head is moved between the area outside the outer periphery of the disk and the area above the disk while the movable end is moved so that the head is farthest away from the disk in a direction vertical to the surface of the disk.
In one preferred embodiment, the moving means is a piezoelectric element.
When the end of the first or second beam opposite to the free end of the first beam, i.e., the proximal end of the first beam or the other end of the second beam, is moved from the first position to the second position, its end positioned to the side of the free end of the first beam is moved so that the head mounted on the free end of the first beam is moved either upward or downward (in other words, the flying height of the head is changed due to the change of the force applied to the free end of the head suspension by the first beam and the second beam).
If the head is moved above the inner area of the disk while the head is farthest away from the disk in a direction vertical to the surface of the disk, the head can be loaded to the disk in its inner area. Since the rotation speed of the disk is slower in its inner area than in the outer area thereof, this inner loading can reduce the level of impact energy generated by the contact of the head with the disk and thereby reduce the degree of damage to the head and to the disk.
Preferably, the disk unit further comprises a negative pressure slider including the head and mounted on the free end of the head suspension and the negative pressure slider generates negative pressure between the surfaces of the disk and the negative pressure slider when the negative pressure slider comes closer to the disk than a predetermined distance.
The negative pressure slider has a bistable flying characteristic, that is, small movement of the negative pressure slider may greatly change the flying height of the head in the vicinity of the predetermined threshold of the flying height. Therefore, the small movement of the negative pressure slider allows for a great change in the flying height of the head, thereby reducing the risk of the head contacting the disk while the head moves to the inner area of the disk.